Excluding Maternal Background Risk in First Trimester Screening – Analysis of a Novel Test Strategy

Objective: As a defined basic risk, the maternal background risk represents the most important influencing factor in the First Trimester Screening (FTS) according to Nicolaides [1–4]. However, the generated risk estimations often deviate from the observed clinical-practical values [5]. The aims of this study were a test performance analysis of the FTS according to Nicolaides and its comparison with the novel "Advanced First Trimester Screening (AFS) ®" algorithm, which explicitly excludes the maternal background risk [5].

Material and methods: At the medical university of Hanover 2,743 pregnancies at 11+0 to 13+6 weeks of gestation underwent a combined ultrasonography and biochemistry First Trimester Screening. In a prospective approach, the risk calculation according to Nicolaides was performed with the classic and the specific algorithm of the ViewPoint-PIA Fetal database (PIA) ^® software [6, 7]. The risk calculation with the AFS^® algorithm was carried out in a retrospective approach.

Results: Both the PIA^® and the AFS^® algorithm reached a sensitivity of 80.00%, a false negative rate of 20.00%, and a negative prediction value of 99.90%. However, with a specificity of 97.01%, a false positive rate of 2.99% and a positive prediction value of 11.76% the AFS^® algorithm showed a better test performance than the PIA^® algorithm (96.06%, 3.94%, and 9.20% respectively).

Conclusion: Within the study population, the elimination of the maternal background risk from the risk calculation generated more precise risk estimations for trisomy 13, 18, and 21. An examination in large, prospective studies may be recommended to consider an introduction of this novel test strategy.